Production method of tire cord steel with high drawing performance

Abstract

The invention belongs to the technical field of steel and iron smelting, and particularly discloses a high-drawing-performance tire cord steel production method which comprises the following steps: firstly, adding a desulfurizing agent into molten iron, stirring for full reaction, and then performing slagging-off treatment on the molten iron; then molten iron is put into a converter to be smelted, and then tapping is conducted; the molten steel is transferred to an LF furnace to be heated, wollastonite and sillimanite are added into the molten steel at the same time, heating is conducted for 5-15 min, sampling is conducted, and then argon is blown into the molten steel to enable the liquid level of the molten steel to slightly vibrate; and then the argon flow is adjusted to be 400 m < 3 > / h, the blowing-in time is smaller than or equal to 30 s, and finally molten steel is injected into a crystallizer. In order to solve the problem that the cord steel product quality is affected due to the fact that the content of inclusions in current cord steel is too high, by optimizing converter smelting, refining and billet continuous casting production process parameters, the proportion of the inclusions in the cord steel is reduced, the content of Al2O3 in the cord steel is reduced, and the problem that when the cord steel is produced, due to the fact that the content of the inclusions in Al2O3 is too high, the cord steel product quality is affected is solved. And the quality of tire cord steel products is poor.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and in particular to a method for producing high-drawing performance cord steel. Background Art

[0002] Cord steel is a high-tech specialty steel primarily used in the manufacture of steel cord. Its development parallels the development of radial tires. Radial tires, using cord steel as their framework, possess a range of excellent properties, including high speed, high load capacity, and durability. As the framework material for radial tires, it is known as the "crown jewel of steel." Its core properties include high cleanliness, high strength, high toughness, and excellent cold working properties, enabling it to withstand the rigors of extreme drawing and twisting processes. It represents one of the technological heights in the metal products industry. With the growth of the automotive industry, demand for cord steel used in radial tire manufacturing continues to increase, placing higher demands on the variety, performance, and quality of steel cord.

[0003] Cord steel, a representative product of ultra-clean steel, is widely used in automotive tire radials, aerospace, and other fields. Its core performance requirements include high strength, high purity, excellent drawing properties, and microstructural uniformity. As the raw material for producing steel cord, the quality of cord steel largely determines its quality. The cleanliness, element segregation level, and especially the morphology of inclusions in cord steel have a significant impact on subsequent products. Non-metallic inclusions can easily cause wire breakage during wire drawing and stranding. Therefore, cord steel must have a small inclusion size and good deformation properties during processes such as rolling and cold drawing. With advances in industrial technology, the application scenarios of cord steel continue to expand, and the performance requirements for products are becoming increasingly stringent. However, existing production processes generally use Si-Mn composite deoxidation, but this involves sources of Al in the alloy and auxiliary materials. The main inclusions in cord steel are MnO-Al2O3-SiO2 and CaO-AlO3-SiO2. Al2O3 is a hard inclusion with a much higher hardness than the cord steel matrix. During cord steel drawing and other processing, this hardness difference causes the matrix around the inclusion to experience significant stress concentration. When the stress exceeds the matrix's bearing capacity, cracks are likely to form at the interface between the inclusion and the matrix, leading to broken cord steel wires and seriously affecting product quality.

[0004] Therefore, in order to solve the above problems, it is necessary to design a production method for cord steel with high drawing performance to reduce the content of Al2O3 inclusions in the cord steel, thereby improving the quality of the cord steel product; and solve the problem that when producing cord steel, the content of Al2O3 inclusions in the cord steel is too high, resulting in cord steel breakage and affecting product quality. Summary of the Invention

[0005] The object of the present invention is to provide a method for producing cord steel with high drawing performance, so as to solve the problem that when producing cord steel, the cord steel wire breaks due to excessively high inclusion content in Al2O3, thereby affecting product quality.

[0006] To achieve the above object, the present invention provides a basic solution: a method for producing high-drawing performance cord steel, comprising the following steps: S1: KR desulfurization: First, add the desulfurizer into the molten iron and stir it for 20-25 minutes to allow the molten iron and the desulfurizer to fully react. Then, skim the molten iron for 5-8 minutes. S2: Converter smelting: The molten iron after slagging is then charged into a converter for smelting. The steel is tapped when the carbon content in the molten iron is ≥0.40%, the phosphorus content is ≤0.018%, and the sulfur content is ≤0.012%. 700kg-750kg of medium carbon ferromanganese, 300kg-350kg of special ferrosilicon, and 400kg-500kg of recarburizer are sequentially added to the molten steel 15s-20s after tapping. S3: LF-RH refining: When the carbon content in the molten steel is 0.66%-0.69%, the molten steel is transferred to the LF furnace for heating. The LF furnace fan speed is 300-320 rpm. Then, 600 kg of wollastonite and 50 kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 5 min-15 min, the molten steel is sampled. If the C content in the molten steel is less than 0.71%, an appropriate amount of recarburizer is added to the molten steel for adjustment. When the molten steel is heated to 1555°C-1560°C, argon is blown into the molten steel to make the molten steel liquid surface vibrate slightly. The argon flow rate is 20-30 m 3 / h, argon blowing time ≥ 30min; S4: Billet continuous casting: Argon is continuously blown into the molten steel after LF-RH refining treatment, and the argon flow rate is adjusted to 400m 3 / h, the argon blowing time is ≤30s, and then the molten steel is injected into the crystallizer. During casting, long nozzle protection casting is performed and the continuous casting machine maintains a constant casting speed, which is 0.70m / min.

[0007] The beneficial effects of the present invention are as follows: (1) The present invention reduces the proportion of Al2O3 inclusions in cord steel by 45% by optimizing the production process parameters of converter smelting, LF-RH refining and billet continuous casting, reduces the presence of Al2O3 in cord steel, and thus improves the drawing performance and processing stability of cord steel. The tensile strength of the steel reaches 1800MPa, the cross-sectional shrinkage (Z) reaches 45%, and the elongation (A) reaches 12%. The produced cord steel can be drawn from φ5.5mm to φ0.16mm without breaking, and the whole (1) The quality of cord steel products is improved and the risk of cord steel wire breakage is reduced; (2) By strictly controlling the molten iron slag removal time, converter melting time and coordination between various processes, the molten steel temperature and heating time are highly matched, which reduces the impact of production rhythm fluctuations on product quality, thereby achieving efficient and stable production; (3) Through standardized control of the entire process from molten iron composition, refining process and billet continuous casting operation, element segregation and abnormal inclusion morphology are effectively suppressed, ensuring the cleanliness and high strength characteristics of cord steel, and meeting the lightweight requirements of radial tires.

[0008] Option 2 is the preferred option of the basic option. In S1, the composition of the molten iron is: Si content is 0.30%-0.40%, P content is ≤0.12%, S content is ≤0.04%, Ti content is ≤0.05%, Cu content is ≤0.025%, As content is ≤0.006%, and the rest is Fe.

[0009] Option three is the preferred option of the basic option. In S2, the amount of molten iron loaded into the converter is 155t-160t, the amount of scrap steel is 20t-30t, and the tapping temperature is ≥1650℃; scrap steel can be used as a coolant to absorb excess heat to control the temperature in the furnace, and can also be used as a metal material supplement. The tapping temperature ≥1650℃ comprehensively guarantees the fluidity of the molten steel and the stability of subsequent processes.

[0010] Option 4 is the preferred option of the basic option. In S2, when the steel is tapped to 2 / 3 of the ladle, a slag stop is placed at the tapping port and the steel is continued. This can effectively reduce the amount of slag during the tapping process, thereby improving the purity and quality of the molten steel.

[0011] Option 5 is the preferred option of the basic option. In S3, the temperature of the molten steel when entering the LF furnace is ≥1525℃. When the temperature of the molten steel entering the furnace is ≤1520℃, 40kg-60kg of calcium carbide is added to the LF furnace; calcium carbide can chemically react with oxygen, sulfur and other substances in the molten steel and release a large amount of heat, thereby providing additional heat for the molten steel, helping to increase the temperature of the molten steel, and thus ensuring the smooth progress of subsequent refining operations.

[0012] Option six is the preferred option of the basic option. In S3, the wollastonite and sillimanite are added in two batches. When the molten steel is heated in the LF furnace for 1 min to 3 min, 300 kg of wollastonite and 50 kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 3 min to 5 min, 300 kg of wollastonite is added. Wollastonite can better absorb inclusions in the molten steel. The application of wollastonite in the refining of cord steel can significantly reduce the content of microscopic inclusions, and the addition of sillimanite to the molten steel can effectively improve the welding performance of the cord steel.

[0013] Option seven is the preferred basic option. In S3, if the carbon content in the molten steel is less than 0.71%, 30kg-50kg of recarburizer is added to the molten steel and stirred for 3 minutes before sampling again. If the refining requirements are not met, 10kg-20kg of recarburizer is added to the molten steel in small amounts and stirred until the C content in the molten steel is 0.71%-0.73%. Adjusting the C content in the molten steel can increase the hardness and strength of the steel, thereby ensuring the performance of the steel.

[0014] Option 8 is the preferred option of the basic option. In S4, when the molten steel is cast, the distance from the protective slag surface to the upper mouth of the crystallizer is ≤50mm, and the total thickness of the protective slag layer is 40mm-50mm; the appropriate protective slag layer thickness can ensure that the protective slag can effectively isolate the air and absorb inclusions.

[0015] Option nine is the preferred option of the basic option. In S4, when the molten steel level is ≤400mm, the casting is stopped and the ladle is changed. After the ladle is changed, 10kg of covering agent is added to the casting hole and then casting is continued. When the molten steel level is lower than 400mm, the casting is stopped, which can effectively prevent the occurrence of slag curling due to liquid level fluctuations. Moreover, as the molten steel level decreases during casting, the fluidity and stability of the molten steel will deteriorate, and uneven casting may occur, thereby affecting the forming quality of the ingot. Therefore, stopping the casting in time can effectively prevent the ingot from having defects such as pores and cracks due to unstable molten steel supply, thereby ensuring the overall quality of the ingot. The covering agent can form a continuous protective layer on the surface of the molten steel, blocking the contact between the molten steel and the air, and reducing the formation of oxide inclusions. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below through specific embodiments: Example 1 A method for producing high-drawing performance cord steel comprises the following steps: S1: KR desulfurization: First, add the desulfurizer into the molten iron with the following components: Si: 0.30%-0.40%, P≤0.12%, S≤0.04%, Ti≤0.05%, Cu≤0.025%, As≤0.006%, and the rest is Fe, and stir for 20min-25min to allow the molten iron and the desulfurizer to fully react. Then, skim the desulfurized molten iron for 5min-8min. S2: Converter smelting: The molten iron after slagging is then charged into the converter for smelting. The amount of molten iron in the converter is 155t-160t, and the amount of scrap steel is 20t-30t. When the C content is ≥0.40%, the P content is ≤0.018%, the S content is ≤0.012% and the temperature is ≥1650℃, steel is tapped. 15s-20s after tapping, 700kg-750kg of medium-carbon ferromanganese, 300kg-350kg of special ferrosilicon and 400kg-500kg of recarburizer are added to the molten steel in sequence. When the molten steel is tapped to 2 / 3 of the ladle, a slag stop is placed at the tapping port to continue tapping. S3: LF-RH refining: When the carbon content of the molten steel is 0.66%-0.69%, the molten steel is transferred to the LF furnace for heating. The LF furnace fan speed is 300-320 rpm. The temperature of the molten steel when entering the LF furnace is ≥1525℃. If the temperature of the molten steel is ≤1520℃, 40-60kg of calcium carbide is added to the LF furnace. When the molten steel is heated in the LF furnace for 1-3 minutes, 300kg of wollastonite and 50kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 3-5 minutes, 300kg of wollastonite is added. When the molten steel is heated in the LF furnace for 5-15 minutes, the molten steel is sampled; if the carbon content in the molten steel is less than 0.71%, 30-50 kg of carburizer is added to the molten steel and stirred for 3 minutes before sampling again. If the refining requirements are not met, 10-20 kg of carburizer is added to the molten steel in small amounts and stirred until the carbon content in the molten steel is 0.71%-0.73%; when the molten steel is heated to 1555-1560 ° C, argon is blown into the molten steel to make the liquid surface of the molten steel vibrate slightly. The argon flow rate is 20-30 m 3 / h, argon blowing time ≥ 30min; S4: Billet continuous casting: Argon is then blown into the molten steel after LF-RH refining treatment, and the argon flow rate is adjusted to 400m 3 / h, argon blowing time ≤30s; then inject molten steel into the crystallizer so that the distance from the protective slag surface to the upper mouth of the crystallizer is ≤50mm; the total slag layer thickness is 40-50mm; during casting, long nozzle protection casting is carried out and the continuous casting machine maintains a constant pulling speed of 0.70m / min; when casting, when the molten steel liquid level is ≤400mm, the casting is stopped.

[0017] The microstructure of the cord steel produced by the above method is mainly sorbite structure, with a content of 87.5%; the grade of network cementite is ≤1, and there is no martensite structure; the grade of non-metallic inclusions of type B (Al2O3) and type D (spherical oxide) in the steel is ≤0.5; the tensile strength of the cord steel is 1800Mpa, the cross-sectional reduction rate (Z) is 45%, and the elongation (A) is 12%; the cord steel produced can be stretched from φ5.5mm to φ0.16mm without breaking.

[0018] Example 2 A method for producing high-drawing performance cord steel, wherein the steps are the same as those in Example 1, except that: S1: KR desulfurization: First, add 1.8t of desulfurizer into molten iron with the following components: C: 4.71%, Si: 0.38%, P: 0.089%, S: 0.021%, Ti: 0.0276%, Cu≤0.025%, As≤0.006%, and the rest is Fe, and stir for 18 minutes. The molten iron temperature is 1307℃ to allow the molten iron and the desulfurizer to fully react. After desulfurization, the S content in the molten iron is 0.0067%. Then, add 400kg of desulfurizer into the molten iron again and stir for 5 minutes. After desulfurization, the S content in the molten iron is 0.005%. Then, skim the molten iron after desulfurization. The skimming standard is that the exposed surface of the molten iron is greater than 95%; S2: Converter smelting: The molten iron after slagging is then charged into a converter for smelting. The amount of molten iron in the converter is 152.5 tons, and the amount of scrap steel is 28 tons. When the C content is 0.533%, the Si content is 0.002%, the Mn content is 0.248%, the P content is 0.018%, and the S content is 0.009% and the temperature is 1540°C, the steel is tapped. S3: LF-RH refining: The molten steel is then transferred to the LF furnace for heating. The temperature of the molten steel when entering the LF furnace is 1565℃. If the temperature of the molten steel is ≤1520℃, 40-60kg of calcium carbide is added to the LF furnace. When the molten steel is heated in the LF furnace for 1min-3min, 312kg of wollastonite and 50kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 3min-5min, 300kg of wollastonite, 160kg of FeSi, 230kg of FeMn and 60kg of recarburizer are added in sequence. Then argon is blown into the molten steel to make the liquid surface of the molten steel vibrate slightly. The argon flow rate is 20-30m 3 / h, and the argon blowing time was 31min.

[0019] The cord steel produced by the above method has a tensile strength of 1840 MPa, a cross-sectional shrinkage rate (Z) of 47%, and an elongation (A) of 13.25%.

[0020] Example 3 A method for producing high-drawing performance cord steel, wherein the steps are the same as those in Example 1, except that: S1: KR desulfurization: First, add 1.8t of desulfurizer into molten iron with the following components: C: 4.93%, Si: 0.32%, P: 0.082%, S: 0.015%, Ti: 0.0447%, Cu≤0.025%, As≤0.006%, and the rest is Fe. The molten iron temperature is 1358℃. Then, turn on the stirring paddle of the desulfurization station and adjust the stirring paddle height so that the stirring paddle is lowered to a height of 4.2m. Then, stir for 6 minutes. Then, adjust the stirring paddle height again so that it is stirred at a height range of 4.2m-4.4m for 14 minutes to allow the molten iron to fully react with the desulfurizer. After desulfurization, the S content in the molten iron is 0.0017%. Then, the molten iron after desulfurization is subjected to slag treatment. The slag skimming standard is that the exposed surface of the molten iron is greater than 95%; S2: Converter smelting: The molten iron after slagging is then charged into a converter for smelting. The amount of molten iron in the converter is 152.1 tons, and the amount of scrap steel is 28 tons. When the C content is 0.577%, the Si content is 0.003%, the Mn content is 0.301%, the P content is 0.015%, and the S content is 0.006%, and the temperature is 1530°C, the steel is tapped. S3: LF-RH refining: The molten steel is then transferred to the LF furnace for heating. The temperature of the molten steel when entering the LF furnace is 1562°C. If the temperature of the molten steel is ≤1520°C, 40-60kg of calcium carbide is added to the LF furnace. When the molten steel is heated in the LF furnace for 1min-3min, 306kg of wollastonite and 50kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 3min-5min, 300kg of wollastonite, 140kg of FeSi, 87kg of FeMn and 60kg of recarburizer are added in sequence. Argon is then blown into the molten steel to make the liquid surface of the molten steel vibrate slightly. The argon flow rate is 20-30m 3 / h, and the argon blowing time was 40min.

[0021] The cord steel produced by the above method has a tensile strength of 1849 MPa, a cross-sectional shrinkage rate (Z) of 46%, and an elongation (A) of 12.75%.

[0022] In summary, the present invention reduces the proportion of Al2O3 inclusions in cord steel by 45% by optimizing the production process parameters of converter smelting, LF-RH refining and square billet continuous casting, reduces the presence of Al2O3 in the cord steel, thereby improving the drawing performance and processing stability of the cord steel. The produced cord steel can be drawn from φ5.5mm to φ0.16mm without breaking, thereby improving the overall quality of the cord steel product and reducing the risk of cord steel breakage; and solves the problem of cord steel breakage and thus affecting product quality due to excessive Al2O3 inclusion content during cord steel production. The tensile strength of the cord steels prepared by the methods in Example 1, Example 2 and Example 3 can all reach above 1800 MPa, the cross-sectional shrinkage (Z) can all reach above 45%, and the elongation (A) can all reach above 12%. Among them, the cross-sectional shrinkage (Z) and elongation (A) of the cord steel prepared by the method in Example 2 are the best, and the tensile performance of the cord steel prepared by the method in Example 3 is the best.

[0023] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for producing high-drawing performance cord steel, characterized in that: The following steps are involved: S1: KR desulfurization: First, add the desulfurizer into the molten iron and stir it for 20-25 minutes to allow the molten iron and the desulfurizer to fully react. Then, skim the molten iron for 5-8 minutes. S2: Converter smelting: The molten iron after slagging is then charged into a converter for smelting. The steel is tapped when the carbon content in the molten iron is ≥0.40%, the phosphorus content is ≤0.018%, and the sulfur content is ≤0.012%. 700kg-750kg of medium carbon ferromanganese, 300kg-350kg of special ferrosilicon, and 400kg-500kg of recarburizer are sequentially added to the molten steel 15s-20s after tapping. S3: LF-RH refining: When the carbon content in the molten steel is 0.66%-0.69%, the molten steel is transferred to the LF furnace for heating. The LF furnace fan speed is 300-320 rpm. Then, 600 kg of wollastonite and 50 kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 5 min-15 min, the molten steel is sampled. If the C content in the molten steel is less than 0.71%, an appropriate amount of recarburizer is added to the molten steel for adjustment. When the molten steel is heated to 1555°C-1560°C, argon is blown into the molten steel to make the molten steel liquid surface vibrate slightly. The argon flow rate is 20-30 m 3 / h, argon blowing time ≥ 30min; S4: Billet continuous casting: Argon is continuously blown into the molten steel after LF-RH refining treatment, and the argon flow rate is adjusted to 400m 3 / h, the argon blowing time is ≤30s, and then the molten steel is injected into the crystallizer. During casting, long nozzle protection casting is performed and the continuous casting machine maintains a constant casting speed, which is 0.70m / min.

2. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S1, the composition of the molten iron is as follows: Si content is 0.30%-0.40%, P content is ≤0.12%, S content is ≤0.04%, Ti content is ≤0.05%, Cu content is ≤0.025%, As content is ≤0.006%, and the rest is Fe.

3. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S2, the converter is loaded with 155t-160t of molten iron and 20t-30t of scrap steel, and the tapping temperature is ≥1650°C.

4. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S2, when the steel is tapped to 2 / 3 of the ladle, a slag stopper is placed at the tapping port and the steel is continued to be tapped.

5. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S3, the temperature of the molten steel when entering the LF furnace is ≥1525°C. When the temperature of the molten steel when entering the furnace is ≤1520°C, 40kg-60kg of calcium carbide is added to the LF furnace.

6. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S3, the wollastonite and sillimanite are added in two batches. When the molten steel is heated in the LF furnace for 1-3 minutes, 300 kg of wollastonite and 50 kg of sillimanite are added to the molten steel. When the molten steel is heated in the LF furnace for 3-5 minutes, 300 kg of wollastonite is added.

7. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S3, if the carbon content in the molten steel is less than 0.71%, 30kg-50kg of recarburizer is added to the molten steel and stirred for 3 minutes before sampling again. If the refining requirements are still not met, 10kg-20kg of recarburizer is added to the molten steel in small amounts and stirred until the C content in the molten steel is 0.71%-0.73%.

8. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S4, when the molten steel is cast, the distance from the protective slag surface to the upper opening of the crystallizer is ≤50 mm, and the total thickness of the protective slag layer is 40 mm-50 mm.

9. The method for producing high-drawing performance cord steel according to claim 1, characterized in that: In S4, when the molten steel level is ≤400mm, the casting is stopped and the ladle is changed. After the ladle is changed, 10kg of covering agent needs to be added into the casting hole and then the casting is continued.